Heliopora coerulea (Blue coral)

Wikipedia Abstract

Blue coral (Heliopora coerulea) is a species of colonial coral and the only species in the family Helioporidae and the only Octocoral known to produce a massive skeleton. This skeleton is formed of aragonite, similar to that of scleractinia. Individual polyps live in tubes within the skeleton and are connected by a thin layer of tissue over the outside of the skeleton. It was described by Pallas in 1766.